Camshaft phasers are used in internal combustion engines in order to vary the timing of the combustion chamber valves so that the phase relation between the crankshaft and the camshaft can be configured variably within a defined angular range between a maximum early position and a maximum late position. Adapting the timing to the current load and rotational speed lowers fuel consumption and reduces emissions. For this purpose, camshaft phasers are integrated into a power train via which a torque is transmitted from the crankshaft to the camshaft. This power train can be configured, for instance, as a belt drive, chain drive or gear drive.
In a hydraulic camshaft phaser, the driven element and the drive element form one or more pairs of pressure chambers that counteract each other and that can be pressurized with oil. Here, the drive element and the driven element are arranged coaxially. A relative movement between the drive element and the driven element is generated by filling and emptying individual pressure chambers. The spring, which has a rotational effect between the drive element and the driven element, forces the drive element relative to the driven element in a preferential direction. This preferential direction can be the same as or opposite to the direction of rotation.
A widespread design of the hydraulic camshaft phaser is the vane-type adjuster. Vane-type adjusters have a stator, a rotor and a drive element. The rotor is usually non-rotatably joined to the camshaft and forms the driven element. The stator and the drive element are likewise non-rotatably joined to each other and, if applicable, are configured in one piece. Here, the rotor is located coaxially to the stator and inside the stator. The rotor and the stator, with their radially extending vanes, form oil chambers that counteract each other, that can be pressurized with oil and that permit a relative movement between the stator and the rotor. Moreover, the vane-type adjusters have various sealing covers. The stator, the drive element and the sealing cover are secured by means of several screwed connections.
Another familiar design of hydraulic camshaft phasers is the axial piston-type phaser. Here, oil pressure serves to axially move a sliding element whose helical gearing generates a relative rotation between a drive element and a driven element.
U.S. Pat. Appln. No. 2009/0173297 A1 discloses a hydraulic camshaft timing device that has a drive gear and, coaxially thereto, a stator with two rotors arranged concentrically to the stator. The stator is configured in one piece or else made up of several components. The rotors and the stator have radially oriented vanes. Owing to these vanes, the stator, together with the rotors, forms working chambers that can be pressurized with a hydraulic medium, so that a relative rotation around the rotational axis of the camshaft phasing device occurs between the appertaining rotor and the stator. A partition wall that is arranged between the rotors separates the rotors axially from each other. Each rotor can be connected to a camshaft. In this case, the camshaft is configured as a hollow shaft, whereas the other camshaft is made of solid material. Both camshafts are arranged concentrically with respect to each other. The cams that are correspondingly associated with the camshafts are joined to their camshaft in such a way that a relative circumferential rotation of the cams or of the individual camshafts can occur relative to each other, so that the timing of the inlet and outlet valves associated with the cams can be adjusted continuously and variably.
The vanes of the rotors and the vanes of the stator have an effective surface which is exposed to pressure when the working chambers are being filled with a hydraulic medium, and thus it is exposed to a force in the circumferential direction that gives rise to the relative rotation. The response behavior of such a hydraulic camshaft phaser is determined by this surface and by the pressure of the hydraulic medium that is generated by a pressure-medium pump.